This invention relates generally to the field of airfoil surfaces and, in particular, to an in-flight, variable geometry and wedge-shaped airfoil utilizable as a control and/or stabilizing surface on high speed aircraft.
In supersonic flight, a fundamental problem is the decay of the lift-curve slope with increasing Mach number. The wedge-shaped airfoil, in current use on certain high speed aircraft, has previously provided significant increases in the said lift-curve slope at low angles of attack and at supersonic Mach numbers. The present invention makes use of the wedge-shaped airfoil by adding a unique and yet simplified variable geometry configuration thereto whereby the airfoil is divided into separate upper and lower airfoil surfaces pivotally mounted at their forward ends for adjustment either individually or in concert between outer or inner positions to thereby control the amount of surface area exposure to the free stream flow to the minimum consistent with effective lift and affording reduced drag and aerodynamic heating. Although the broad concept of airfoils having separate upper and lower "trailing edge" surfaces adjustable between inner and outer positions has been previously developed as is illustrated, for example, in FIG. 25 of a U.S. Pat. No. 1,854,444, issued Apr. 19, 1932 to G. E. Barnhart, it is obvious from an examination of said patent that what appears, at first glance, to be a similar device is actually an arrangement involving a different principle of operation in that by the outward movement of the Barnhart trailing edge surfaces at 6 and 41 to their extended relation, a higher pressure distribution over the said surfaces is thereby generated. Moreover, the retracted position of the Barnhart trailing edge surfaces 6 and 41 is actually the normal streamlined position. On the other hand, the novelty of the present invention resides, first, in its combination with the high speed wedge-shaped airfoil, secondly, the application of the separated relation between the upper and lower airfoil surfaces of the inventive arrangement to all or substantially all of the entire airfoil, unlike the application of the separated airfoil surfaces 6 and 41 (FIG. 25) of Barnhart to the trailing edge only, to thereby provide a positive control of the pressure distribution over the entire airfoil, and lastly and, perhaps, most importantly, the pivotally mounted and separate airfoil surfaces of the present invention are adjustable to a retracted position further inwardly of the normal streamlined position, unlike Barnhart, to be thereby shielded from and thus expose less surface area to the free stream flow for providing reduced drag and aerodynamic heating at the retracted surface, as will appear self-evident hereinafter in the following summary and detailed description.